No ETA yet. I had been doing some major work to clean up the DG evaluation. This would be a prerequisite of getting parallel DG to work. After that I'd probably have a better idea of the work that's involved in running under parallel DG.

However, note that even when parallel DG is supported, it doesn't mean that assets can evaluate in parallel. Evaluating multiple assets will still happen in a serial fashion. Evaluating multiple assets in parallel would likely require adding support for running multiple backends.

The benefit of supporting parallel evaluation is to allow multiple Maya nodes to evaluate simultaneously. So this doesn't stop Houdini Engine's internal cooking to be multithreaded. And like Houdini's cooking, Houdini Engine's internal cooking is already multithreaded. So there's likely not much benefit from the Houdini Engine side.

But since the global evaluation mode needs to be set to “DG” in order for Houdini Engine evaluate correctly, this means no Maya nodes can make use of parallel evaluation, which is a performance improvement in recent Maya versions. So the main benefit for Houdini Engine to support parallel evaluation is to allow other Maya nodes to evaluate in parallel if those nodes support it.

So the performance benefit would depend entirely on what nodes are in a Maya scene. I suspect there's not much benefit if the Maya scene is mostly doing dynamics. Maya scenes that have heavy rigging and animation might be the ones that see performance improvement. The best way to see whether there would be improvement is probably to take a Maya scene that doesn't use Houdini Engine, and toggle between DG and Parallel evaluation mode.